The present invention relates to a light beam scanning device for scanning a laser beam in an application where a delicate and precise operation is to be carried out with the laser beam under an operating microscope.
To perform a delicate and precise operation on the human body with a laser knife, in general, a light beam scanning device incorporating a movable mirror is mounted on the front part of an operating microscope and a laser beam is reflected by the movable mirror into the field of vision of the microscope to illuminate the desired location. In order to direct the laser beam to a desired point in the field of vision, it is necessary to scan the laser beam by slightly turning the movable mirror vertically or horizontally. In general, the movable mirror is disposed on the optical axis of the objective lens of the operating microscope and in front of the objective lens forming an angle of 45.degree. with the optical axis. After being reflected by the movable mirror, the incident laser beam advances along the optical axis to the desired point of illumination.
On the other hand, it is necessary for the operator to locate the part to be operated on in the field of vision of the microscope at all times and hence the laser beam must be collimated and accurately applied. Moreover, the movable mirror should not obstruct the field of vision.
The right and left sides of the circular field of vision of the objective lens of the microscope are filled by the rays which form the fields of vision of the right and left eyepieces of the microscope, respectively, and the upper part of the circular field of vision of the objective lens is used to apply light for illuminating the field of vision. Accordingly, in the field of vision of the objective lens, only the central part and a slit-shaped part below the center are available for the reflection of the laser beam.
Taking these facts into account, movable mirrors have been designed having various configurations and dimensions. A conventional movable mirror is provided with a transparent glass plate large enough to cover the diameter of the objective lens. The central portion of the transparent glass plate is formed as a small circular portion on which a metal film is deposited by vacuum evaporation with the circular portion being large enough to reflect a laser beam. Such a movable mirror, which is necessarily large in size, is supported by a mirror supporting frame which includes a mechanism for rotating the mirror around the horizontal and vertical axes thereof. Accordingly, the mirror supporting frame must be larger than the movable mirror. The rotating mechanism is, in general, a gimbal mechanism and the movable mirror is turned by operating an operating lever which is rotatable around the gimbal fulcrum.
In such a light beam scanning device, the space in front of the objective lens is occupied by the large movable mirror and therefore the gimbal part is disposed at the righthand side in the housing of the device. Accordingly, the device is quite long in the widthwise direction.
Light beam scanning devices of this type have been disclosed by Japanese Laid-Open Patent Application Nos. 8085/1974 and 8997/1979.
It is desirable to reduce the size and weight of the device by decreasing both the width and depth as much as possible due to the following reasons. An operation using a laser beam under microscope is often carried out with the aid of an endoscope extended to the part to be operated on. The focal distance of the objective lens of the device ranges from 200 mm to 400 mm. However, it is desirable that the distance between the objective lens and the incidence end of the endoscope be long enough to facilitate the operation. The endoscope requires a minimum length to be suitable for performing most operations. Accordingly, the depth of the light beam scanning device, namely, the thickness in the direction of the optical axis, must be made as small as possible. Furthermore, the width of the device should be as small as possible because the spaces on the right-hand side and left-hand side of the objective lens are used to carry out auxiliary operations during the operation.
Accordingly, an object of the invention is to provide a light beam scanning device small in size and light in weight in which its movable mirror is so dimensioned as not to obstruct observation through an operating microscope and the illumination range of the microscope, its width and depth are so small that the device does not obstruct an operation, and the rotational movement of the movable mirror around any one or both of the horizontal and vertical axes is smoothly carried out without interference.